如题，代码：

#include<bits/stdc++.h>
using namespace std;
int n,l,r,h[10005],ans,minh,x;
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;i++)scanf("%d",&h[i]);
	l=1;r=n;
	while(h[l]==0)l++;
	while(h[r]==0)r--;
	x=l;
	for(int i=l;i<=r;i++)
	{
		if(h[x]>=h[x+1])
		{
			int st=x;
			while(h[x]>=h[x+1]&&x<=r)x++;
			while(h[x]<=h[x+1]&&x<=r)x++;
			if(x>r)break;
			int en=x;
			minh=min(h[st],h[en]);
			for(int i=st+1;i<en;i++)ans+=(minh-h[i]);
		}
		i=x=max(i,x);
	}
	printf("%d",ans);
	return 0;
}